Vestibular function is to be investigated in cats and humans. In cats we shall examine responses of second order brain stem vestibular neurons and eye movements to labyrinthine stimulation. Single semicircular canals are to be stimulated by angular acceleration given precisely in the planes of the canals and given at different angles to the canal planes. Thresholds and the range of angulation over which the horizontal, anterior and posterior canals respond will be determined. The different response characteristics for certain types of vestibular neurons--Type I, Type II, tonic and kinetic--units will be compared. In humans, single semicircular canals are to be stimulated by angular acceleration, given precisely in the planes of the canals and at different angles to the canal planes. Eye movements will be monitored by electronystagmography.